The determination of absolute geographic directions by means of an optronic imaging device which does not have an orientation device allowing for a direction measurement of quality compatible with that sought, is a technological challenge.
In effect, the systems which attempt to resolve this problem generally use orientation measurement components whose cost remains high to achieve the performance sought which can be of the milli-radian class. For example, an angular performance of 1 milli-radian class to 90% is necessary to contain a location error in the category TLE1 (6 m at 90%) on an object situated at 5 km from the sensor. The orientation measurement devices of this class are rare, expensive and too heavy to be considered in a portable device.
The following solutions which make it possible to measure attitude are not well suited for the following reasons:                magnetic compasses are inefficient (10 milli-radians class), difficult to incorporate, highly sensitive to the EM environment, use the local magnetic declination (it also being poorly known in the 10 milli-radians class) to transform the magnetic azimuth into geographic azimuth or direction, their cost is relatively low, but can be as high as 1000.        FOGs (acronym for Fiber Optic Gyrometer), laser gyrometers (RLGs), hemispheric resonator gyrometers (HRGs), are bulky, heavy, heavy electrical consumers and expensive,        The MEMS are not sufficiently efficient (a few milli-radians), exhibit low maturity and require a calibration procedure that can be lengthy and complex,        the celestial objects allow high performance but are not always visible (difficulty seeing the stars in day time, or the sun through heavy clouds),        the positioning systems such as GNSS (acronym for global navigation satellite system), are moderately positioned for the length bases envisaged, and their volume, their weight and their consumption are incompatible with a portable device,        the use of landmarks often extracted from data of ortho-image (line of sight equivalent to a vertical view) or map type, is not easy to implement when using an image of opportunity (above all when it is small field and a glancing shot) since:                    this approach first of all requires the availability of the vertical view with the good level of detail,            the probability of being able to map a landmark point with a detail present in the image reduces quadratically with the field thereof,            the probability of being able to associate several landmarks in an image decreases linearly with their number.The technique based on the polarization of the sky, a recent technique bio-inspired from the orientation of insects for their navigation, offers low performance levels.                        